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| Paper: |
The RR Lyrae Instability Strip in the Split Horizontal Branch Globular
Cluster NGC 6569 |
| Volume: |
491, Fifty Years of Wide Field Studies in the Southern Hemisphere: Resolved Stellar Populations in the Galactic Bulge and the Magellanic Clouds |
| Page: |
104 |
| Authors: |
Kunder, A.; Stetson, P. B.; Catelan, M.; Walker, A.; Cassisi, S.; Johnson, C.; Soto, M. |
| Abstract: |
The first calibrated broadband BVI\/ time-series photometry is obtained
for the RR Lyrae variable stars in the split horizontal branch (HB) cluster
NGC 6569. As a result, a sizeable population of 27 RR Lyrae variables
has been identified. An eclipsing binary in the RR Lyrae instability strip
was also found, which is most likely a field star. The 12 fundamental-mode
RR Lyrae variables (RR0) have an average period of [P]RR0=
0.57±0.02 d and the 15 first-overtone variables (RR1) have an average
period of [P]RR1=0.30±0.01 d. The mean periods of the
RR Lyrae stars are consistent with an Oosterhoff I designation, and the number
ratio of RR1- to RR0-type variables, N1/NRR=0.56, is more consistent
with an Oosterhoff II designation. Compared to the M3 variables, the
NGC 6569 RR Lyrae variables are not shifted to a longer periods at a given
amplitude, making it unlikely that these stars are He-enhanced. The similarity
in the periods and amplitudes between the RR Lyrae stars in NGC 6569 and
the bulge field RR Lyrae population may indicate similar formation conditions. |
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